CHAPTER XXIII 



ROUNDWORMS: NEMATHELMINTHES 



Very close and diligent looking at living creatures, even through the best 

 microscope, will leave room for new and contradictory discoveries. 



George Eliot 



Ascaris. As'caris lumbricoi'des is often found as a para- 

 site in the intestine of man. The body, which is cylindrical 

 and tapering at both ends, is frequently over ten inches in 

 length and in diameter as large as an ordinary lead pencil. 

 The sexes are separate, and the male is always considerably 

 smaller than the female. For a long time it was thought that 

 this parasite was relatively harmless. Very recently it has 

 been found that the young when taken into the digestive 

 tract with food or water do not become established there at 

 once as parasites. They first wander around, boring their 

 way through various organs of the body. In young pigs 

 they pierce the lungs in such numbers as to cause a dis- 

 ease resembling pneumonia. In the human being, Ascaris 

 is especially likely to occur in small children. This is due 

 to the fact that young children are not careful about what 

 goes into their mouths. Food dropped onto polluted soil con- 

 taining Ascaris eggs readily brings the eggs into a child's 

 mouth. Whether we are interested in saving children or 

 pigs from the ravages of Ascaris the same methods apply. 

 Sanitary surroundings are not favorable for the worms. 



The structure of Ascaris is very simple. The digestive 

 tract runs as a straight tube throughout the length of the 

 body. The cavity between the digestive tract and the body 

 wall is filled with the coils of the reproductive organs. 



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